I have supported frankenstien projects like this since I was a kid always taking apart the off the shelf 'toys' and seeing what I could do to modify them. So I would like to offer you some help. It's going to sound like severe criticism, but it's just intended to get the point across and it involves your choice of wheels and tires.
The wheels and tires can and often do play a part in impact absorbsion. The wheels and tires you got on there might look cool, and may have been cheap (I noticed your budget is limited) but when you land that thing you midas well have stone wheels on it as they would be softer then those things!
Here is a pic of whats on my rc10 gold tub truck conversion.. yes it's driven daily, and yes it got a bath after this pic LOL!
Those are HPI mags but someone else here would have to cough up the model because they came with the truck and I have no idea. The tires are run of the mill tamiya all traction utilities found on the pumpkins, lunchboxes, etc. You can still get them new for about 25.00 a set of 4. They would actually fit right on your rims should you want to keep them, and will stance wider. The sidewalls are short, not tall so they will lower the CG a hair, but the extra width puts more tire on the ground.
The key here is to let some of your tires/wheels pre-absorb some of that impact to soften the blow to the suspension systems. I have a kyosho tracker here with the wheels/tires you use and they are entirely too hard for they're own good. Not only are those mags/tires that I run about 10x softer, they track better and break dirt lose better from the tracks as it rolls. They dig well and provide serious cushioning as well. I have never collapsed one completely under hard acceleration, wear is minimal, and the combo weighs in MUCH less then what your currently using. Not to mention they would look sick on your truck! They are 'genderized' so you need to order two sets of rears for your 4wd and they would bolt right up using hex adapters.
If you need to go bigger, try the clodbuster originals. Same tires, just BIGGER. Not sure they make a nice mag aftermarket rim for those though, might be stuck with the tamiya solids and adapters. Another thing to mention is what you cannot actually see with your eyes. Those mags will also absorb some impact in comparison to the solid wheels, another thing to consider. I'm willing to bet a careful changeup of your wheel/tire combo will yield a lighter, better handling and more durable vehicle. I have those wheels/tires that your running on my tracker basher and that chassis/suspension system buckles before they even break a squat out of the sidewalls. Just ridiculously useless tires.. rotational wobble.. high mass.. etc.. I just hate those damn things.. LOL
Save your pennies and ditch 'em. You will thank me.